Sanicro® 69

Disclaimer: Recommendations are for guidance only, and the suitability of a material for a specific application can be confirmed only when we know the actual service conditions. Continuous development may necessitate changes in technical data without notice. This datasheet is only valid for Sandvik materials.

Sanicro® 69 is an austenitic nickel-chromium-iron alloy used primarily for steam generators in nuclear power plants (PWR). For this application it is used in the 'thermally treated' condition. This treatment results in chromium carbide precipitation at the grain boundaries but no significant chromium depletion. The grade has good structure stability and good weldability.

For the steam generator application the material is characterized by:

Extremely high resistance against stress corrosion cracking in primary side PWR water conditions

Forms of supply

Tube and pipe are delivered in the solution annealed and pickled condition.

PWR steam generator tubes are delivered in the bright annealed and thermally treated condition. The thermal treatment involves a treatment in vacuum furnace at about 720°C (1330°F) for normally 10 hours.

Mechanical properties

The following two tables give general nominal values.At 20°C (68°F)

Proof strengthRp0.2a)MPa

ksi

Tensile strengthRmMPa

ksi

ElongationAb)%

HardnessVickersapprox.

≥240

≥35

≥585

≥85

≥30

160

1 MPa = 1N/mm2a)Rp0.2 corresponds to 0.2% offset yield strength.b) Based on L0 = 5.65 ÖS0 where L0 is the original gauge length and S0 the original cross-section area.At high temperatures

Temperature

Proof strength

Tensile Strength

°C

°F

Rp0.2

Rm

MPa

ksi

MPa

ksi

min.

min.

min.

min.

100

210

220

31.9

550

79.8

200

390

190

27.5

510

74.0

300

570

187

27.1

495

71.8

400

750

184

26.7

490

71.1

500

930

180

26.1

480

69.6

600

1110

175

25.4

440

63.8

700

1290

150

21.8

340

49.3

For steam generator tubing in the thermally treated condition the following higher proof strength values can be guaranteed.

Temperature

Proof strength

°C

°F

Rp0.2

MPa

ksi

20

68

280

40.6

100

210

260

37.7

200

390

240

34.8

350

660

210

30.5

Impact strengthSince Sanicro® 69 is a fully austenitic alloy it possesses good toughness down to -196°C (-320°F)

Physical properties

Density: 8.12 g/cm3; 0.293 lb/in3

Thermally Treated condition

Specific heat capacity

Temperature, °C

J/(kg °C)

Temperature, °F

Btu/(lb °F)

23

460

73

0.11

100

480

200

0.11

200

495

400

0.12

300

505

600

0.12

400

510

800

0.12

500

520

1000

0.13

600

580

1100

0.14

Thermal conductivity

Temperature, °C

W/(m °C)

Temperature, °F

Btu/(ft h°F)

23

11

73

6.5

100

13

200

7.5

200

14

400

8.5

300

16

600

9.5

400

18

800

10.5

500

19

1000

11.5

600

23

1100

13

Resistivity

Temperature, °C

μΩm

Temperature, °F

μΩin.

20

1.11

68

43.7

100

1.14

200

44.9

200

1.18

400

46.5

300

1.22

600

48.0

400

1.24

800

48.8

Thermal expansion 1)

Temperature, °C

Per °C

Temperature, °F

Per °F

30-100

13.5

86-200

7.5

30-200

14

86-400

8

30-300

14.5

86-600

8

30-400

15

86-800

8.5

30-500

15.5

86-1000

8.5

30-600

15.5

86-1200

9

1) Mean values (x10-6)

Modulus of elasticity 1)

Temperature, °C

MPa

Temperature, °F

ksi

20

210

68

30.5

100

206

200

30.0

200

201

400

29.1

300

195

600

28.1

400

189

800

27.1

500

182

1000

26.0

600

174

1200

24.8

1) (x103)

Corrosion resistance

Stress corrosion cracking

The thermally treated condition of Sanicro® 69 is developed specifically to resist stress corrosion cracking in steam generator environment at nuclear power plants. This has been confirmed by laboratory stress corrosion cracking tests in pure water (less than 5 ppm oxygen, 4-5 ppm hydrogen added) at 365°C (690°F).

No stress corrosion cracking was developed in Sanicro® 69 during the entire test period of 33 000 hours. Alloy 600 started to crack after 200 hours.

Heat treatment

For steam generator application the tubes are delivered in the thermally treated conditions. This means exposure at about 720°C (1330°F) for normally 10 hours. Prior to the thermal treatment the tubes are solution annealed at approximately 1100 °C (2010°F) for some minutes.

For other applications the tubes are delivered in the solution annealed condition. If additional solution annealing is necessary after further processing the following procedure is recommended:

1050-1150°C (1920-2100°F), 1-10 minutes, rapid cooling in air or water.

Welding

Sanicro® 69 has good weldability. Suitable welding methods are manual metal-arc welding with covered electrodes and gas shielded arc welding, such as TIG and MIG. Strip overlay welding of tube sheets can be made using ESW. Preheating and post-weld heat treatment are normally not necessary.

This type of nickel-base materials have increased risk of hot cracking compared to standard stainless steels. Therefore welding should be performed with low heat input and with low dilution from the base material to reduce the risk of hot cracking. It is also important to keep the joint surfaces and the welding material as clean as possible, for the same reason. These measures are especially important when the weldment is under constraints.

Since Sanicro® 69 has low thermal conductivity and high thermal expansion, a low heat input is also important for reducing the deformation and residual stresses in the welded joint.

As filler metal for TIG and MIG welding Sanicro® 68HP is recommended. For manual metal-arc welding, covered electrode Sanicro 69 is the first choice. For strip overlay welding Sanicro® 69HP is recommended.

Fabrication

Bending

The excellent formability of Sanicro® 69 permits cold-bending to very small bending radii. Annealing is normally not necessary after cold-bending owing to the high stress corrosion cracking resistance for Sanicro® 69.

Expanding

Sanicro® 69 is expanded into tube sheets in the same way as standard austenitic stainless steels.

Applications

Steam generators in nuclear power plants.

Units in contact with nitric acid at elevated temperatures.

Equipment requiring high resistance to oxidation, carburization and nitriding.

Units exposed to caustic solutions at high temperature.

Disclaimer: Recommendations are for guidance only, and the suitability of a material for a specific application can be confirmed only when we know the actual service conditions. Continuous development may necessitate changes in technical data without notice. This datasheet is only valid for Sandvik materials.